JP2013054968A - Lithium ion battery and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion battery having excellent high-rate discharge characteristics and high safety.SOLUTION: On at least one of a surface or a rear face of a positive electrode current collector, a cathode active material mixture layer containing a solid flame-resistant agent is coated to form a coating layer, and the coating layer is dried under a dry condition, in which deposit precipitates toward the positive electrode current collector while keeping the coating layer in a posture positioned above the current collector. The dry condition includes the drying temperature and drying time determined so that the flame-resistant agent deposited within the drying time precipitates.

Description

  The present invention relates to a lithium ion battery including an electrode plate in which an active material mixture layer containing a flame retardant is formed on a current collector, and a method for manufacturing the same.

  Lithium ion batteries have a high energy density, and volatile organic solvents are used as non-aqueous electrolytes. Therefore, when the lithium ion battery is placed in a high temperature environment, or when it overheats, overdischarges, or when an internal short circuit occurs, the battery bursts and expands due to the increase in the internal pressure of the battery due to the vaporization of the nonaqueous electrolyte. In addition, there is a problem that the battery ignites and emits smoke due to combustion of the non-aqueous electrolyte and the positive electrode active material. In order to solve these problems, in the conventional lithium ion battery, the safety of the battery is improved by various methods. In Patent Document 1 (Japanese Patent Laid-Open No. 5-151971, paragraph [0012]), a slurry is prepared by adding a flame retardant to a paste-like positive electrode mixture, and this is applied in a thin layer on both surfaces of a core material. A technique for forming a positive electrode plate by drying a sheet formed in this manner is disclosed. In Patent Document 2 (Japanese Patent Laid-Open No. 2009-16106), a slurry in which a powdery flame retardant is dispersed almost uniformly is applied to a current collector, dried, and then rolled to make the flame retardant. An invention in which an agent is dispersed in a positive electrode mixture layer is disclosed.

JP-A-5-151971 JP 2009-16106 A

  In the conventional lithium ion batteries disclosed in Patent Documents 1 and 2, since a flame retardant is present in the positive electrode material mixture layer, battery rupture, ignition, and the like during abnormal heat generation can be suppressed. However, the presence of the flame retardant inhibits ion permeability in the positive electrode mixture layer and increases the electric resistance between the active materials, so that there is a problem that battery performance such as high rate discharge characteristics is deteriorated.

  An object of the present invention is to provide a lithium ion battery having good high rate discharge characteristics even when a flame retardant is present in an active material mixture layer.

  Another object of the present invention is to provide a lithium ion battery that can increase the flame retardance of the battery as compared with the prior art.

  An object of the present invention is to provide a production method that can easily produce a lithium ion battery having good high rate discharge characteristics and higher flame retardance than conventional ones.

  The lithium ion battery to be improved by the present invention includes a positive electrode plate in which a positive electrode active material mixture layer containing a solid flame retardant is formed on at least one of the front and back surfaces of a positive electrode current collector. Prepare. The positive electrode current collector is usually composed of an aluminum foil. Lithium ion batteries use a flammable non-aqueous electrolyte. It is known that a positive electrode active material such as spinel lithium manganate decomposes while releasing oxygen at a high temperature in a charged state. The released oxygen accelerates the combustion of the electrolyte. It is presumed that the flame retardant supplements radicals generated in the combustion process and has a function when the chain reaction is terminated. As a result, since the chain reaction of radicals generated in the combustion process is suppressed, it is possible to achieve flame retardancy of the lithium ion battery.

  In particular, in the lithium ion battery of the present invention, the abundance ratio of the flame retardant in the region near the positive electrode current collector side is more than the abundance ratio of the flame retardant in the region near the surface of the positive electrode active material mixture layer. The positive electrode plate is configured to be large. In such a structure, since the flame retardant present on the surface side of the positive electrode active material mixture layer is small, lithium ions easily enter the positive electrode active material mixture layer from the surface of the positive electrode active material mixture layer. Therefore, according to the lithium ion battery of the present invention, battery characteristics (battery performance such as high rate discharge, low rate discharge, life, and charging) can be improved while achieving flame retardancy of the battery. In addition, in the structure of the present invention, since there are many flame retardants on the positive electrode current collector side in the positive electrode active material mixture layer, radicals generated in the combustion process during abnormal heat generation become flame retardant near the positive electrode current collector. It becomes easy to be trapped in the agent. Aluminum used as the positive electrode current collector is easily combusted during abnormal heat generation, and has a large heat of combustion. Therefore, the temperature tends to be high, and is most easily combusted in the vicinity of the positive electrode current collector in the positive electrode active material mixture layer. For this reason, when the structure in which the radicals are easily trapped in the vicinity of the positive electrode current collector as in the present invention, combustion is easily suppressed at the portion where the positive electrode active material mixture layer easily burns, and the flame retardancy of the battery is made higher than before. Can be increased.

  The lithium ion battery of the present invention has a structure in which the abundance ratio of the flame retardant increases as it approaches the positive electrode current collector. Thus, when the flame retardant in the positive electrode active material mixture layer is unilaterally biased to the positive electrode current collector side, the active material mixture layer in the vicinity of the current collector in the positive electrode active material mixture layer Since it is possible to prevent an increase in electrical resistance, it is possible to suppress deterioration of battery characteristics such as high rate discharge characteristics.

  In the present invention, it is preferable to use a flame retardant having a melting point of 90 ° C. or higher. In addition, the flame retardant having a melting point of less than 90 ° C. is liable to be entirely or partially liquid even when the lithium ion battery is normally used (when no abnormal heat generation occurs). Therefore, since it cannot exist stably in a positive electrode active material mixture layer, there exists a possibility of causing the fall of battery characteristics (battery performance, such as high rate discharge, low rate discharge, lifetime, charge).

As the flame retardant having such a melting point, a cyclic phosphazene compound represented by the general formula (NPR ₂ ) ₃ or (NPR ₂ ) ₄ can be used. R in the general formula represents a halogen element such as fluorine or chlorine or a monovalent substituent. As monovalent substituents, alkoxy groups such as methoxy group and ethoxy group, aryloxy groups such as phenoxy group and methylphenoxy group, alkyl groups such as methyl group and ethyl group, aryl groups such as phenyl group and tolyl group, Examples thereof include an amino group containing a substituted amino group such as a methylamino group, an alkylthio group such as a methylthio group and an ethylthio group, and an arylthio group such as a phenylthio group.

  Further, in the method for producing a positive electrode plate used in the lithium ion battery of the present invention (method for producing an electrode plate for a lithium ion battery), when the solvent volatilizes in a state where it is first dissolved in the solvent and dissolved in the solvent. Prepare a solid that precipitates and becomes solid at room temperature. A slurry obtained by mixing this flame retardant with a positive electrode active material, a conductive agent, and a binder in a solvent is applied to the positive electrode current collector to form a coating layer. And a coating layer is dried on the dry conditions which hold | maintain the attitude | position in which an application layer is located above a positive electrode electrical power collector, and a deposit settles toward an electrical power collector. Of course, it may be rolled after drying.

  In the conventional method of manufacturing a lithium ion battery shown in Patent Document 2, since the active use of the precipitation of the flame retardant is not considered, drying is completed before the flame retardant settles. It is thought that. Therefore, it is considered that the flame retardant is present almost uniformly in the positive electrode active material mixture layer. According to the method of the present invention, since the drying conditions are determined so that the precipitated flame retardant is collected on the current collector side by sedimentation, the abundance ratio of the flame retardant in the positive electrode active material mixture layer is A positive electrode plate having a larger abundance ratio in a region closer to the positive electrode current collector than a presence ratio in a region near the surface of the agent layer can be easily produced.

  As a method of forming a flame retardant layer on the positive electrode current collector side, a flame retardant is applied on the positive electrode current collector separately from the positive electrode active material mixture, and then a positive electrode active material mixture layer is formed. In principle, this method is also conceivable. However, this method has a problem that the manufacturing method is complicated and control is difficult. Further, special measures are required to form a structure in which the abundance ratio of the flame retardant increases as it approaches the positive electrode current collector. Then, the positive electrode plate of this invention can be manufactured by one application | coating process by using the manufacturing method of this invention.

  Convection is unlikely to occur in the coating layer during drying. Then, if the coating layer is dried so that the precipitates settle, a positive electrode plate in which the flame retardant is unevenly distributed on the current collector side in the positive electrode active material mixture layer can be obtained with certainty.

  The drying conditions in which the flame retardant settles while precipitating can be determined as appropriate. For example, drying at a relatively low temperature for a relatively long time can be considered.

  In addition, the drying temperature can be changed stepwise. For example, it is conceivable that drying is performed at a low temperature for a long time in the initial stage of drying, and the temperature is increased when the drying speed is lowered to speed up drying and increase productivity. In this way, it is possible to shorten the time until the drying is completed while precipitating the deposited flame retardant.

  Conversely, there is a method of drying at a relatively high temperature in the initial stage and lowering the temperature when the drying speed is lowered. In this case, although the effect is lower than the former two, a certain degree of effect can be obtained and the time to completion of drying can be shortened.

  When the preset temperature of the drying furnace is high and drying is performed rapidly, temperature distribution may occur in the positive electrode active material mixture layer. Convection occurs when the temperature distribution in the positive electrode active material mixture layer is large. Convection is thought to impede sedimentation of precipitates. Therefore, when the set temperature is lowered and dried slowly, an electrode plate in which the flame retardant settles and the flame retardant is unevenly distributed on the positive electrode current collector side can be obtained with certainty. On the other hand, when drying from the inside of the positive electrode active material mixture layer as in microwave drying, the drying becomes uniform and convection may not easily occur. Therefore, it is presumed that an electrode plate for a lithium ion battery in which a flame retardant is present on the positive electrode current collector side as in the present invention can be produced without determining the drying temperature and the drying time as described above. The

(A) is the schematic shown in the state which saw through the inside of the laminated battery used as a lithium ion battery of this invention, (B) is the IB-IB sectional view taken on the line of (A). It is a graph which shows the relationship between the distance (arbitrary unit) from a positive electrode electrical power collector, and the density | concentration (arbitrary unit) of phosphorus in the inside of the positive electrode plate of the lithium battery (laminate battery) which is embodiment of this invention. It is a graph which shows the relationship between the distance (arbitrary unit) from a positive electrode electrical power collector, and phosphorus concentration (arbitrary unit) in the inside of the positive electrode plate of the lithium ion battery (laminated battery) which is a comparative example of this invention.

  Hereinafter, embodiments of the present invention will be described in detail. FIG. 1A is a schematic view showing the inside of a laminate battery as an embodiment of the lithium ion battery of the present invention in a transparent state, and FIG. 1B is a diagram of IB-IB in FIG. It is sectional drawing. The lithium ion secondary battery (laminated battery 1) includes a positive electrode plate 3 having a positive electrode lead terminal 3a, a negative electrode plate 5 having a negative electrode lead terminal 5a, and a separator disposed between the positive electrode plate 3 and the negative electrode plate 5. 7 and a non-aqueous electrolyte 9 in which a lithium salt is dissolved in an organic solvent. The positive electrode plate 3, the negative electrode plate 5, and the separator 7 are laminated to constitute an electrode plate group 11 made of a laminate. The electrode plate group 11 is housed in the case 13 with the positive electrode lead terminal 3a and the negative electrode lead terminal 5a being connectable to the outside. The inside of the case 13 is evacuated with the nonaqueous electrolyte 9 filled. In this example, such a lithium ion secondary battery (laminated battery 1) was produced as follows.

[Non-aqueous electrolyte]
A non-aqueous electrolyte 9 is injected into the case 13. As the nonaqueous electrolytic solution 9, a solution obtained by dissolving lithium tetrafluoroborate as a lithium salt in a mixed solvent of ethylene carbonate and dimethyl carbonate in a volume ratio of 1: 1 at 1.5 mol / liter is used. .

[Production of positive electrode plate]
The positive electrode plate 3 uses an aluminum foil as a positive electrode current collector. The thickness of the aluminum foil is set to 20 μm in this example. A positive electrode active material mixture containing a lithium transition metal double oxide as a positive electrode active material is applied to the front and / or back surface of the aluminum foil. In this example, lithium manganate powder having a spinel crystal structure is used as the lithium transition metal double oxide. In addition to the positive electrode active material, the positive electrode active material mixture includes carbon powder as a conductive material, polyvinylidene fluoride (hereinafter referred to as PVDF) as a binder (hereinafter referred to as PVDF), and powder (solid) as a flame retardant. A phosphazene compound is blended. In this example, the blending ratio of the lithium manganate powder, carbon powder, PVDF, and flame retardant powder is set to 85: 5: 5: 5 (% by weight). That is, the blending ratio of the flame retardant to the positive electrode active material mixture is set to 5% by weight. When a positive electrode active material mixture is applied to an aluminum foil, the viscosity is adjusted with a dispersion solvent N-methyl-2-pyrrolidone (hereinafter referred to as NMP) to prepare a slurry. The flame retardant is dispersed in this slurry. This slurry is applied to a positive electrode current collector made of an aluminum foil to form a coating layer. Then, the coating layer is dried while maintaining the posture in which the coating layer is positioned above the current collector. In the present invention, the drying conditions (drying temperature, drying time, drying method, etc.) are determined so that the flame retardant deposited in the coating layer settles on the positive electrode current collector side as in the examples described later. After drying, press working was performed to produce a positive electrode sheet. Such a positive electrode sheet was cut into 10 cm × 20 cm, and a current collecting tab of aluminum foil was welded to prepare a positive electrode plate 3.

[Flame retardant (phosphazene compound)]
The flame retardant used in the production of the positive electrode plate is a phosphazene compound, which precipitates when the NMP solvent volatilizes in a state dissolved in the NMP solvent and dissolved in the NMP solvent. As such a phosphazene compound, a cyclic compound represented by the general formula (NPR ₂ ) ₃ or (NPR ₂ ) ₄ can be used. In the present embodiment, Phoslite AE (registered trademark) manufactured by Bridgestone Corporation was used. In this cyclic phosphazene compound, R in the general formula is phenoxy, is solid at room temperature, and has a melting point of about 110 ° C.

[Production of negative electrode plate]
The negative electrode plate 5 uses a copper foil as a negative electrode current collector. The thickness of the copper foil is set to 10 μm in this example. A negative electrode active material mixture containing a carbon material such as amorphous carbon powder or graphite powder capable of occluding and releasing lithium ions as a negative electrode active material is applied to the front and back surfaces of the copper foil. In addition to the negative electrode active material, PVDF is blended in the negative electrode active material mixture as a binder. Although the flame retardant is not blended in the negative electrode active material mixture of this example, when the flame retardant is blended, the same phosphazene compound as that blended in the positive electrode active material mixture can be used. In this example, the blending ratio of the carbon material and PVDF is set to 90:10 (% by weight). A slurry is prepared while adjusting the viscosity by dispersing the carbon material and PVDF thus set in an NMP solvent. This slurry is applied to a copper foil negative electrode current collector and dried in the same manner as in the case of preparing a positive electrode plate. After drying, press working was performed to prepare a negative electrode sheet. The negative electrode sheet was cut to 10 cm × 20 cm, and a nickel foil current collecting tab was welded to the cut sheet to prepare the negative electrode plate 5.

[Create laminate]
The positive electrode plate 3, the negative electrode plate 5, and the separator 7 are laminated with the separator sheet (separator 7) made of polyethylene sandwiched between the positive electrode plate 3 and the negative electrode plate 5 thus manufactured, and the battery capacity becomes 8 Ah. Thus, an electrode plate group 1 was produced.

[Battery assembly]
The prepared electrode plate group 11 is inserted into an outer packaging material (which will later become a case 13) made of a heat-sealing film (aluminum laminate film), and the prepared non-aqueous electrolyte 9 is placed in the outer packaging material. Injected into. Then, the inside of the exterior material was evacuated, and the opening of the exterior material was quickly heat-sealed to produce a flat lithium ion battery (laminated battery 1).

  Next, examples of the lithium ion battery (laminated battery 1) according to the present embodiment will be described. A comparative lithium ion battery (laminated battery) produced for comparison will also be described.

[Example 1]
In the present embodiment, the drying conditions are determined so that the flame retardant precipitates during the drying time during the production process of the positive electrode plate.

  Specifically, it was formed by applying a positive electrode active material mixture containing the aforementioned cyclic phosphazene compound to the surface of the positive electrode current collector under the drying conditions of a drying temperature of 100 ° C. and a drying time of 260 seconds. The coating layer was dried, and the positive electrode plate 3 of the lithium ion secondary battery 1 was produced.

  In Example 1, the drying temperature (100 ° C.) was lower than the melting point (110 ° C.) of the cyclic phosphazene compound. Further, the drying time (260 seconds) was set to a length capable of completing constant rate drying and decreasing rate drying at a constant temperature (100 ° C.). This drying time makes it possible to deposit the flame retardant while allowing the flame retardant to settle, rather than drying the coating layer early.

  As in the comparative example described later, when drying is performed at 120 ° C. for 100 seconds, drying occurs before settling, or settling is prevented due to convection, so the flame retardant is contained in the mixture. Disperse almost evenly.

[Example 2]
In this example, in the process of manufacturing the positive electrode plate, heating was performed at a relatively low temperature as an initial drying condition, and the temperature was increased at the time when the evaporation rate of the solvent was lowered, that is, at the stage where the reduction drying process was reached. . When such drying conditions are employed, the deposited flame retardant can be allowed to settle, and the time until completion of drying can be shortened.

  Specifically, in the process of manufacturing the positive electrode plate 3, the initial drying furnace set temperature was set to 100 ° C. The drying rate decreased after 100 seconds from the start of drying. At that time, the preset temperature of the drying furnace was raised to 120 ° C. Drying was completed after 50 seconds.

[Example 3]
In this example, heating is performed at a relatively high temperature as an initial drying condition in the manufacturing process of the positive electrode plate. The drying temperature was lowered when the drying rate decreased.

  Therefore, in Example 3, specifically, the initial drying furnace set temperature was set to 120 ° C. in the manufacturing process of the positive electrode plate. The drying speed decreased 50 seconds after the start of drying. At that time, the preset temperature of the drying furnace was lowered to 100 ° C. Drying was completed after 130 seconds.

[Comparative Example 1]
In this comparative example, the surface of the positive electrode current collector under the drying conditions substantially employed in Patent Document 2 described above using a positive electrode active material mixture that does not contain a flame retardant (cyclic phosphazene compound). The coating layer formed by applying the positive electrode active material mixture to was dried to prepare a positive electrode plate of a lithium ion secondary battery. Specifically, drying conditions were set such that the preheating temperature was 120 ° C., the preheating time was 50 seconds, the drying temperature was 120 ° C., and the drying time was 100 seconds.

[Comparative Example 2]
Under the same drying conditions as in Comparative Example 1, the coating layer formed by applying a positive electrode active material mixture containing a flame retardant (cyclic phosphazene compound) to the surface of the positive electrode current collector was dried to produce a positive electrode plate To form a lithium ion secondary battery.

[Comparative Example 3]
A positive electrode active material containing a flame retardant (cyclic phosphazene compound) on the surface of the positive electrode current collector under the same drying conditions as in Comparative Example 2 except that the preheating temperature and the preheating time were changed with respect to Comparative Example 2. The coating layer formed by applying the mixture was dried to produce a positive electrode plate of a lithium ion secondary battery. Specifically, the drying conditions were set to a preheating temperature of 100 ° C., a preheating time of 70 seconds, a drying temperature of 120 ° C., and a drying time of 100 seconds.

(Internal observation of positive electrode plate)
The inside of the positive electrode plate produced as an Example and a comparative example was observed. The inside of the positive electrode plate was observed using an electron beam microanalyzer (EPMA-1600) manufactured by Shimadzu Corporation to measure the distribution of the flame retardant inside the positive electrode plate (FIGS. 2 and 3). 2 and 3 are graphs showing the relationship between the distance from the positive electrode current collector (arbitrary unit) and the phosphorus concentration (arbitrary unit) inside the positive electrode plates of Example 1 and Comparative Example 2. FIG. From this graph, the phosphorus concentration that changes from the positive electrode current collector side inside the positive electrode plate toward the surface side of the positive electrode active material mixture layer is measured, and the positive electrode of the cyclic phosphazene compound (flame retardant) containing phosphorus The degree of distribution in the active material mixture layer was confirmed. In addition, about the comparative example 3, although the graph which shows the distribution degree of the flame retardant in the inside of a positive electrode plate is not shown in particular, the inside of the positive electrode plate of the comparative example 3 is the same as the inside of the positive electrode plate of the comparative example 2. The structure was confirmed. Also, for Examples 2 to 4, the graph showing the distribution of the flame retardant inside the positive electrode plate is not particularly shown, but the inside of the positive electrode plate of Examples 2 to 4 is the inside of the positive electrode plate of Example 1. It was confirmed that the structure was the same.

(Evaluation of battery characteristics / High rate discharge test)
The battery characteristics were evaluated when the positive electrode plates produced as examples and comparative examples were used for lithium ion secondary batteries (laminated battery 1). The battery characteristics were evaluated by a high rate discharge test. In the high-rate discharge test, first, a charge / discharge cycle with a current of 1.6 A is repeated twice in a voltage range of 4.2 to 3.0 V under an environment of 25 ° C., and the battery is further charged to 4.1 V. went. After charging, each rate discharge was measured at currents of 1.6 A (0.2 CA), 8 A (1 CA), 16 A (2 CA), and 24 A (3 CA). The final voltage was 3.0V. Table 1 shows the relative capacity (%) at 24 A (3 CA) discharge with respect to the capacity at 1.6 A (0.2 CA) discharge.

(Evaluation of flame retardancy / nail penetration test)
A nail penetration test was conducted on the batteries when the positive electrode plates produced as examples and comparative examples were used for lithium ion secondary batteries. In the nail penetration test, first, the battery was charged to 4.2 V by repeating the charge / discharge cycle under the same conditions as in the high-rate discharge test. Thereafter, under the same temperature condition of 25 ° C., a ceramic nail having a shaft diameter of 5 mm was pierced perpendicularly to the center of the side surface of the battery at a speed of 1.6 mm / s, and the temperature and voltage were monitored. Table 1 shows the maximum temperature reached.

(Comprehensive evaluation)
As a result of high-rate discharge test and nail penetration test, if the relative capacity (%) of 3CA discharge to 0.2CA capacity is high and the maximum temperature (° C) at the time of nail penetration is suppressed to a low level, ○ When it was not satisfied on the other hand, it was set as x.

  As shown in Table 1 and FIG. 3, as a result of observing the inside of the positive electrode plate, the flame retardant (cyclic phosphazene compound) is in the positive electrode active material mixture layer in Comparative Example 2 and Comparative Example 3 dried at a high temperature. It was confirmed that they were dispersed almost uniformly in the positive electrode active material mixture layer regardless of the positive electrode current collector side and the surface side. On the other hand, as shown in Table 1 and FIG. 2, in Examples 1 to 3 dried at a low temperature in all or part of the drying step, the flame retardant (cyclic phosphazene compound) is a positive electrode active material mixture. It was found that there was almost no presence on the surface side in the layer, and there was an uneven distribution on the positive electrode current collector side. Furthermore, in Examples 1 to 4, the degree of distribution increases as the flame retardant (cyclic phosphazene compound) in the positive electrode active material mixture layer approaches the current collector side from the surface side of the positive electrode active material mixture layer. (See Fig. 2).

  From these results, by performing drying at a low temperature in all or part of the drying process, the abundance ratio of the flame retardant in the region near the current collector side is in the region near the surface of the positive electrode active material mixture layer. It has been found that a positive electrode plate can be formed which is larger than the existing ratio of the flame retardant and the increasing ratio of the flame retardant becomes closer to the current collector. In Comparative Example 2 and Comparative Example 3 in which the preheating temperature and the preheating time are different from each other, the positive electrode plate in which the flame retardant (cyclic phosphazene compound) is biased to the positive electrode current collector side in the positive electrode active material mixture layer is Since it was not obtained, it turned out that the preheating conditions before drying do not follow the conditions for obtaining the structure of this invention.

  Further, as a result of the high rate discharge test and the nail penetration test, in Comparative Example 1 in which the positive electrode active material mixture layer does not contain a flame retardant, the high rate discharge capacity is maintained, but in the nail penetration test When the internal short circuit was performed, the maximum temperature reached was extremely high. In addition, fuming was observed. In Comparative Examples 2 and 3, since the flame retardant (cyclic phosphazene compound) was included in the positive electrode active material mixture layer, the maximum temperature reached was kept low. In addition, no smoke or ignition was observed. However, since the flame retardant (cyclic phosphazene compound) is almost uniformly dispersed in the positive electrode active material mixture layer, the high rate discharge capacity is low. On the other hand, Examples 1-3 provided with the positive electrode plate in which a flame retardant (cyclic phosphazene compound) exists in the positive electrode collector side in the positive electrode active material mixture layer (is unevenly distributed) have a high rate discharge capacity. Was good, and the maximum temperature reached when nailing was low. In addition, no smoke or ignition was observed. From these results, it is possible to use a positive electrode plate in which the flame retardant (cyclic phosphazene compound) is unevenly distributed on the positive electrode current collector side in the positive electrode active material mixture layer, so that the lithium ion battery does not deteriorate high rate discharge characteristics. It was found that the safety of can be improved.

  Although the embodiments and examples of the present invention have been specifically described above, the present invention is not limited to these embodiments and examples, and modifications based on the technical idea of the present invention are possible. Of course.

  According to the present invention, since the abundance ratio of the flame retardant in the positive electrode active material mixture layer is small in the region close to the surface of the positive electrode active material mixture layer, lithium ions are present on the surface of the positive electrode active material mixture layer. Can easily enter the positive electrode active material mixture layer. In addition, since there are more flame retardants in the region closer to the positive electrode current collector than in the region closer to the surface side of the positive electrode active material mixture layer, radicals generated in the combustion process during abnormal heat generation are It becomes easy to be trapped by the flame retardant near the body. Therefore, according to the present invention, a lithium ion battery having good high rate discharge characteristics and higher flame retardancy than the conventional one can be obtained.

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 3 Positive electrode plate 5 Negative electrode plate 7 Separator 9 Nonaqueous electrolyte 11 Electrode plate group 13 Case

Claims (5)

A positive electrode plate in which a positive electrode active material mixture layer containing a solid flame retardant is formed on at least one of the front and back surfaces of the positive electrode current collector when the battery abnormally generates heat due to overcharge or overdischarge. A lithium ion battery comprising:
Lithium, wherein the abundance ratio of the flame retardant in the region near the positive electrode current collector side is larger than the abundance ratio of the flame retardant in the region near the surface of the positive electrode active material mixture layer Ion battery.   2. The lithium ion battery according to claim 1, wherein an abundance ratio of the flame retardant increases as it approaches the positive electrode current collector.   The lithium ion battery according to claim 1, wherein the flame retardant has a melting point of 90 ° C. or higher.   The lithium ion battery according to claim 3, wherein the flame retardant is a cyclic phosphazene compound. A method for producing an electrode plate for a lithium ion battery in which a positive electrode active material mixture layer containing a flame retardant is formed on at least one of the front and back surfaces of a positive electrode current collector,
Prepare a solid flame retardant that precipitates as a precipitate when the solvent volatilizes in a state dissolved in the solvent and dissolved in the solvent,
Applying a slurry in which the flame retardant is mixed with the solvent together with a positive electrode active material, a conductive agent, and a binder to the positive electrode current collector to form a coating layer,
The coating layer is dried under a drying condition in which the coating layer is maintained in a position above the positive electrode current collector and the precipitate is settled toward the positive electrode current collector. Manufacturing method of electrode plate for lithium ion battery.

Images